Graft-versus-host disease occurs in patients with aplastic anemia, leukemia, or other diseases who have received bone marrow transplants from non-identical donors. A major impediment to successful bone marrow transplantation is the presence of immunocompetent T lymphocytes in the donor graft which lead to the development of graft-versus-host disease (GVHD). GVHD frequently results in high morbidity and death. T-cells in the donor marrow react against the host and cause the GVHD. The problem in the past has been that elimination of the T-cells in order to prevent the disease has also produced damage to the bone marrow stem cells. Previous attempts at controlling graft-versus-host disease has centered on the use of complement plus antibody to kill the T-cells in bone marrow. However, complement has been shown to be not suitable for clinical use since it is difficult to standardize and is frequently toxic to human bone marrow stem cells. Antibody by itself, that is, without the complement, is not toxic enough to prevent GVHD.
The preliminary experiments, conducted on mice, illustrated that GVHD could be substantially prevented (anti-Thy 1.1) by binding the toxin ricin to monoclonal antibody anti-Thy 1.1 or anti-Thy 1.2. These experiments produced an assortment of moieties which prevented GVHD in mice. Some use anti-Thy 1.1 or anti-Thy 1.2 with intact ricin, others with the A chain or B chain of ricin, and others with ricin A chain followed by separate treatment with ricin B chain. In each case, the problem was the same--transporting a toxic amount of ricin across the cell wall and into the cytosol compartment where protein is made. These experiments showed (on mice) that an efficient pathway involved the application of ricin linked to anti-Thy 1.1 or anti-Thy 1.2 in a medium containing excess lactose, or ricin A chain linked to anti-Thy 1.1 plus an excess of ricin B chain added separately. (Neville and Youle, Ser. No. 350,222 and Ser. No. 350,223, both filed Feb. 19, 1982).
The application of these experiments to humans, however, is not clear-cut, thus providing the substance of this application. Humans require a different monoclonal antibody directed toward T-cells; however, such antibody must have sufficient affinity and receptor sites to efficiently direct the toxin to the cytosol compartment. The T-cell specific reagent preferred, but not limited thereby, is TA-1. Like Thy 1.1 and Thy 1.2, TA-1 is a well-known and easily produced monoclonal antibody and is commercially available from Hybritech, LaJolla, Calif. (Roitt, I., Essential Immunology, Blackwell Scientific Publications, 1980, Chapters 3 and 4). Human bone marrow is removed from the donor, incubated with TA-1-ricin, and placed into the human irradiated patient.
Ser. No. 186,735 (filed Sept. 30, 1980), now allowed, teaches the use of Thy 1.2-ricin on murine lymphoma cancer and is hereby incorporated by reference.
The present application teaches a human T-cell specific hybrid protein which selectively kills T-cells in human bone marrow samples without damaging the bone marrow stem cells.